Applicant has previously proposed a water-disintegratable cleaning sheet having water-disintegratable paper impregnated with an aqueous cleaning agent (see JP-A-2-149237), in which the water-disintegratable paper is made by wet papermaking and contains a water soluble binder having a carboxyl group, and the aqueous cleaning agent contains a polyvalent metal ion and an organic solvent as essential ingredients. Applicant has also proposed a water-disintegratable cleaning article having water-disintegratable paper impregnated with a boric acid aqueous solution containing a water soluble solvent (see JP-A-3-292924), in which the water-disintegratable paper is made by wet papermaking and contains polyvinyl alcohol as a binder. These water-disintegratable cleaning articles have strength withstanding cleaning operation and good water disintegratability making them flushable. The water-disintegratable paper, i.e., a fibrous base sheet, of these water-disintegratable cleaning articles is made of non-heat-fusible and biodegradable cellulosic materials such as pulp to develop post-disposal water disintegratability.
In order to secure post-disposal biodegradability of water-disintegratable paper for applications inclusive of the cleaning articles, it is difficult to use heat fusible fiber that is generally non-biodegradable. Although fiber of biodegradable polylactic acid, etc. is among heat fusible fibers, such biodegradable fiber is expensive and not economical. Pulp is typical of biodegradable and inexpensive fibers.
Means for making paper made mainly of pulp bulky for applications inclusive of the cleaning articles include embossing between engraved rolls. Paper embossing techniques are roughly divided into dry embossing effected on dry paper and wet embossing effected on a wet fiber web on a papermaking machine before drying (see JP-A-8-260397). JP-A-8-260397 mentions that an embossed wet fiber web is dried in a drying step. In order to remove a quantity of water from a wet fiber web from a papermaking step, it is necessary to bring the wet web in contact with a yankee dryer or a multi-cylinder dryer to achieve high thermal efficiency. When such a drying method is adopted, it has been impossible to highly emboss the wet web to create high bulk. On the other hand, dry embossing, which is most commonly practiced, is effected on paper obtained by drying a wet fiber web from a papermaking step. When paper made primarily of non-heat-fusible fiber such as pulp is embossed, paper undergoes destruction of the fiber-to-fiber bonds (including hydrogen bonds and bonding via a binder), or fibers break. This results in reductions of paper strength and embossed shape retention (bulk retention). In applications as water-disintegratable cleaning articles, the dry embossed paper is subject to various external forces while it is processed into a final product, such as folding, cutting, impregnation with a cleaning solution, packaging, and container filling. In the meantime, the bulk created by the embossing is reduced. The tendency to the reductions in paper strength and bulk during post-embossing processings and cleaning operation is conspicuous where paper is highly embossed.